1. Field of the Invention
The present invention relates to an ink remaining amount detecting device that detects the amount of ink remaining in an ink tank, a method for detecting the amount of remaining ink, and an ink jet printing apparatus with an ink remaining amount detecting function.
2. Description of the Related Art
Ink tanks in which ink to be supplied to an ink jet printing apparatus is stored are now known to be in various forms. Examples of forms in which ink is stored in an ink tank include a sponge scheme of storing the ink in the ink tank by allowing the ink to permeate a sponge housed inside the ink tank, a real tank scheme of storing the ink directly inside the ink tank, and a bag scheme of storing the ink in a flexible bag. The sponge scheme involves the sponge placed inside the ink tank and thus a reduced amount of stored ink with respect to the volume. Furthermore, the bag scheme involves the need to protect the bag in which the ink is housed with a casing, thus reducing the amount of stored ink with respect to the overall volume. The real tank scheme has the highest volumetric efficiency. However, even ink tanks adopting the real tank scheme pose the following challenges regarding a function to detect the amount of ink remaining inside the ink tank.
In general, ink jet printing apparatuses have a function to, for example, warn a user or shut down the ink jet printing apparatus when the amount of remaining ink reaches a specified threshold value. Such a warn function, shutdown function, and the like act importantly in preventing possible inappropriate printing caused by a shortage of ink. On the other hand, the function may make a user dissatisfied with the inability to use a certain amount of ink remaining. To avoid such dissatisfaction, a remaining amount detecting device is required which can constantly accurately detect a small amount of ink.
Examples of current remaining amount detecting devices that detect the amount of ink remaining in the ink tank include a dot count scheme, a float scheme, and a prism scheme. The dot count scheme counts the number of ink ejections based on image data to calculate the amount of remaining ink based on the count value, and has the advantage of eliminating the need to add components. However, the ejection amount of nozzles may be varied by a variation in the temperature of a print head, a variation among manufactured products, or the like, resulting in a great difference between actual ink consumption and calculated ink consumption.
Furthermore, the float scheme uses a configuration in which a float migrating according to the level of the ink is placed in the ink tank and in which an optical sensor senses the position of the ink. This configuration disadvantageously requires a large space and is unsuitable for detecting a small amount of ink.
On the other hand, the prism scheme provides a triangle pole-shaped prism formed of a transparent resin member inside the ink tank so that the presence or absence of the ink is detected by detecting the presence or absence of light reflected by the prism to which the light has been delivered. An optical sensor with a light emitting element and a light receiving element irradiates the prism with light and detects reflected light. According to the prism scheme, light delivered toward the prism by the light emitting element enters the interface between the inside of the ink tank and the prism at an angle of 45°. The light entering the interface at an angle of 45° penetrates the interface between the resin and the ink, while being reflected by the interface between the resin and air due to a difference in refractive index. As a result, when an amount of ink is present, the light emitting element fails to detect light. When no ink is present, light is reflected and the reflected light is detected by the light receiving element. Thus, an output signal from the light receiving element allows the presence or absence of ink in the ink tank to be detected.
As described above, the prism scheme directly detects the position of the level and is thus more accurate than the dot count scheme. Moreover, advantageously, the prism itself can be molded integrally with other members using resin, and can thus be appropriately recycled and formed to be small.
However, the prism scheme poses the following problems. That is, if the ink tank is left stationary over a long period, the ink may adhere to the surface of the prism. As a result, even when the ink in the ink tank is exhausted, erroneous detection of the presence of ink may be caused by the ink adhering to the prism surface. To avoid such erroneous detection, emission intensity may be increased. However, disadvantageously, when the amount of remaining ink is detected with the emission intensity kept high, the life of the light emitting element is significantly shortened. Furthermore, a common method for preventing a possible increase in load on the light emitting element is to apply a water repellent to the prism surface in order to smoothly remove the ink that is in contact with the prism surface. However, precisely applying the water repellent to the prism surface is difficult, disadvantageously complicating manufacturing steps and increasing the cost of the ink tank.
Furthermore, as a method of avoiding the use of a water repellent, a technique has been disclosed which forms a groove laterally to the prism so that the capillary force of the groove can draw the ink adhering to the prism surface into the groove for removal (Japanese Patent Laid-Open No. 2000-71471). However, the technique disclosed in Japanese Patent Laid-Open No. 2000-71471 has difficulty molding a fine groove laterally to the prism and thus needs to overcome practicability and accuracy problems.
Moreover, a technique has been disclosed which sets the emission intensity of the light emitting element to a large value so that reflected light from an ink tank with the lowest reflectance can be detected based on information from the light receiving sensor (Japanese Patent Laid-Open No. 2003-89218). However, the technique disclosed in Japanese Patent Laid-Open No. 2003-89218 emits light with a high emission intensity not only to an ink tank with a low reflectance but also to an ink tank with a high reflectance. Thus, disadvantageously, the life of the light emitting element is significantly reduced.